Mariah Carey, Nick Cannon -- Absence Makes the Heart Fonder ... But Not That Fond

Mariah Carey and Nick Cannon are actually getting along -- way better than when they were together and loathed each other -- but TMZ has learned there is NO chance of a reconciliation.

TMZ first reported ... the divorce is a "done deal" and the couple has been separated since May.

We're told they are not only on good terms -- primarily for the sake of their kids -- they even went to dinner Friday in Tribeca and shockingly no one even noticed.

It's a big improvement from 6 months ago, when there was so much contempt they literally could not be in the same room together.

We're told it's all about the kids ... they're both committed to making the divorce as easy as possible on them. But -- let's just say one side tells us -- they will NEVER get back together.